1. Field of the Invention
The invention relates to a method and to a device for generating hot combustion waste gases, in particular to a gas turbine system having an oxygen separation device that receives a portion of combustion waste gas and feeds oxygen from an oxygen-containing gas to the waste gas which is then fed with a fuel or fuel/steam mixture to a burner for catalytically initiated or stabilized combustion.
2. Background of the Invention
EP 0 882 486 A1 discloses a device of the above-mentioned type provided with a burner whose outlet side is connected to a waste gas line, from which a return line branches off. In this burner, a combustion that generates hot combustion waste gases takes place. These combustion waste gases exit the burner through the waste gas line, whereby one part of the combustion waste gases is branched off via the return line. The device is provided with an oxygen separation device, the first inlet of which is connected to the return line, and the second inlet of which is connected to a gas supply that provides oxygen-containing gas. The oxygen separation device therefore is supplied with branched-off or returned waste gas via its first inlet, and with oxygen-containing gas, for example concentrated ambient air, via its second inlet. The oxygen separation device contains oxygen separation means, for example an ion transport membrane. These oxygen separation means remove oxygen from the oxygen-containing gas and supply it with the branched off waste gas, so that the oxygen content of the oxygen-containing gas is reduced, and oxygen-enriched, branched-off waste gas is generated. The oxygen separation device is provided with a first outlet for the oxygen-enriched, branched-off waste gas as well as a second outlet for the gas that has been reduced with respect to its oxygen content. An inlet side of the burner is connected to the first outlet of the oxygen separation device as well as to a fuel supply that supplies fuel. In this manner, a combustion mixture that burns in the burner while forming the desired hot combustion waste gases is created no later than in the burner. The combustion gases generated in this manner can be used, in particular, in a gas turbine system in order to generate electrical energy.
By using such a device or method, it is possible to reduce noxious emissions during energy generation, in particular to significantly reduce CO2 emissions during the combustion of fossil fuels.
The core concept of these methods and devices is that pure oxygen is used as an oxidant for the combustion, since this greatly simplifies the waste gas after treatment. The reason for this is that a combustion process with molecular oxygen provides a waste gas that essentially consists only of CO2 and H2O. Since oxygen, which is produced in refrigerated plants, is very expensive, new technologies have been developed for oxygen production. Important factors hereby are oxygen separation devices that are provided with a membrane that is conductive for oxygen ions and electrons, a so-called MCM membrane (mixed conducting membrane). Such an MCM membrane has a retention side on which the oxygen-containing gas is located and a pass-through side on which the gas to be enriched is located. The MCM membrane transports oxygen ions from the retention side to the pass-through side and causes an electron transport from the pass-through side to the retention side. For this purpose, oxygen is removed from the gas on the retention side and is supplied to the gas on the pass-through side. In order to increase the conductivity of such a MCM membrane, it is advantageous to set a relatively high flow speed on the pass-through side in order to keep the oxygen concentration on the pass-through side as low as possible. A high flow speed on the pass-through side results only in a relatively small enrichment of the returned waste gases with oxygen, however, so that this oxygen/waste gas mixture shows only weak reactance and is not suitable for standard combustion methods.
U.S. Pat. No. 5,976,223 discloses a method and a device for producing carbon dioxide and oxygen. Into a first oxygen separation device working with a MCM membrane, compressed, heated, and oxygen-containing gas is introduced on the retention side. On the pass-through side, a gaseous fuel is supplied that reacts with the added oxygen and forms carbon dioxide. The oxygen-containing gas whose oxygen-content has been reduced is heated by the exothermic reaction taking place hereby. The oxygen-containing gas heated in this manner is then fed to a second oxygen separation device working with an MCM membrane on its retention side. The desired oxygen then collects on the pass-through side of this second oxygen separation device.
WO 98/55394 describes a method in which an oxygen separation device working with an MCM membrane is used as a burner in order to produce hot combustion waste gases for a gas turbine system. Hereby ambient air is compressed, heated, and fed to the retention side of this membrane reactor. A mixture of returned waste gas and fuel is fed to the retention side. Then oxygen is removed from the fed-in air in the membrane reactor and is fed into the mixture. On the pass-through side, the fuel then reacts with the oxygen on the membrane surface that is coated with an oxidation catalyzer. The resulting hot waste gases are then fed to a turbine.
WO 98/55208 discloses a further method for the production of hot combustion gases for the operation of a turbine, in which compressed fresh air is heated in a first burner and is fed to the retention side of a oxygen separation device working with an MCM membrane. Returned waste gas is fed together with fuel to a second burner that may be constructed as a catalyzer. The combustion gases generated there are then fed to the pass-through side of the oxygen separation device, where they are enriched with oxygen. The waste gases enriched with oxygen are then fed to a third burner and burned there with fuel in order to generate hot combustion gases that drive a turbine.
The invention at hand concerns the objective of disclosing for a method or device of the initially mentioned type an embodiment that has a higher efficiency.
According to the invention, this objective can be realized by a method for producing hot combustion waste gas, comprising the steps of producing a hot combustion waste gas by combustion in a burner that is catalytically initiated or stabilized, feeding a first portion of the combustion waste gas to a first inlet of a first oxygen separation device, feeding an oxygen-containing gas to a second inlet of the first oxygen separation device, removing oxygen from the oxygen-containing gas by an oxygen separation means of the first oxygen separation device and reducing an oxygen content of the oxygen-containing gas, feeding said oxygen to the first portion of the combustion waste gas and oxygen enriching an oxygen content of the first portion of the combustion waste gas, and feeding the oxygen-enriched, first portion of the combustion waste gas and a fuel or a fuel/steam mixture to the burner to form a combustion mixture that burns in the burner in the step of producing the hot combustion waste gas. This procedure allows the combustion mixture to react adequately even in the presence of relatively low oxygen concentrations in order to produce the desired hot combustion waste gases.
Since this means that a relatively low oxygen content in the combustion mixture will be sufficient, the flow speed of the returned waste gases can be increased on the pass-through side of an oxygen separation device working with an MCM membrane, increasing its efficiency and thus the efficiency of the entire process.
The objective underlying this invention is also realized with a device for producing a hot combustion waste gas, comprising a burner comprising an outlet side, an inlet side, and a catalyzer that initiates or stabilizes a combustion and a first oxygen separation device comprising a first inlet, a second inlet, a first oxygen separation means that removes oxygen from an oxygen-containing gas and feeds the oxygen to a branched-off waste gas, a first outlet for the oxygen-enriched, branched-off waste gas, and a second outlet for the reduced oxygen-containing gas. The outlet side of the burner is connected to a waste gas line from which a return line branches off, the inlet side of the burner operatively communicates with the first outlet of the first oxygen separation device and a fuel supply line to supply a fuel or a fuel/steam mixture, the first inlet of the first oxygen separation device is operatively connected with the return line, and the second inlet of the first oxygen separation device is operatively connected to a gas supply line to supply the oxygen-containing gas. The divide also creates the possibility of burning combustion waste gases with a relatively low oxygen content in order to generate the desired hot combustion waste gases. As explained above, this makes it possible to increase the efficiency during the production of the hot combustion waste gases. With an integration of the device according to the invention or the method according to the invention into a gas turbine system, the latter""s efficiency also can be increased.
In a further development, a second oxygen separation device may be provided, whereby the non-branched-off or non-returned part of the hot combustion waste gases as well as fuel or fuel/steam mixture are fed to a first inlet of this second oxygen separation device and hereby form a mixture, and whereby the oxygen-containing gas that has been reduced with respect to its oxygen content is fed to a second inlet of this second oxygen separation device, whereby this second oxygen separation device also is provided with oxygen separation means, for example an MCM membrane, that is able to remove yet even more oxygen from the oxygen-containing gas and feed it into the mixture, whereby the mixture on the one hand burns with the oxygen and produces hot combustion waste gases, while on the other hand a gas that has again been reduced with respect to its oxygen content and heated, i.e. oxygen-poor gas, is produced. These measures make it possible to provide both hot combustion waste gas as well as hot, oxygen-poor gas, which can be used, for example, in a following gas turbine system for the production of electricity. Because of the higher starting temperatures that can be achieved, this results overall in a higher efficiency for the overall system.
In a preferred further development, the catalyzer of the burner can be designed as a metal oxide catalyzer. Suitable metals belong, for example, to the perovskite family, e.g. Lal-xSrxBO3, whereby the B side contains elements of the transition metals, for example Mn, Fe, Co. Simple metal oxides from Mn or Ce also can be used. Metal oxide catalyzers are characterized by their high heat resistance, but in contrast to noble metal catalyzers require higher inlet temperatures, which in the present case do exist, however.
Catalyzers with a monolithic carrier and parallel flow channels were found to be advantageous. Such catalyzers are characterized by their relatively low flow resistance. Catalyzers of this type are used, for example, in waste gas cleaning systems of vehicles, in so-called xe2x80x9c3-wax catalyzers.xe2x80x9d
In an especially advantageous embodiment, the burner may be connected in a heat-transferring manner with a heat exchanger that heats the oxygen-containing gas prior to its entrance into the oxygen separation device. The heat exchanger, for example, forms the outer sleeve of the burner, achieving an especially high efficiency for the heat exchanger.
Preferred is a first embodiment in which the oxygen separation device has a first chamber and a second chamber, and in which the oxygen separation means are provided with a membrane, for example an MCM membrane, that separates the two chambers from each other and transports oxygen from one chamber into the other chamber. Particularly advantageous hereby is an embodiment in which the flow passes through both chambers in the same direction and parallel to the membrane. This flow in the same direction makes it possible to create a relatively low temperature profile in the membrane, both parallel to the flow and vertical to it. As a result, thermal loads are reduced.
A gas turbine system comprises the device for producing a hot combustion waste gas and a first gas turbine for generating electricity, the first gas turbine in operative communication with the device to receive the hot combustion waste gas. A second gas turbine can also be in operative communication with the device. The second gas turbine can be connected to a compressor to compress the oxygen-containing gas prior to entry into the device and can be connected to a generator for electrical generation.